The role of areal heat capacity and decrement factor in case of hyper insulated buildings: An experimental study

•A preliminary study was performed to select a range of internal linings with increasing thermal capacity and decreasing decrement factor.•Three panels were simultaneously tested on the south wall of a hyper-insulated and lightweight test room: the envelopes were monitored yearly.•The heat transfer through each portion of the south wall was assessed under different internal heat loads and throughout the seasons.•The comparative analysis highlighted that medium-high thermal capacity linings represented the best practice in Mediterranean climate. Extensive simulation-based researches have highlighted the importance of placing a massive layer in the inner side of hyper insulated CLT buildings in the interest of optimize their thermal performance on an annual basis. The purpose of the present research is to experimentally evaluate the thermal responsiveness of multi layered and highly insulated CLT building envelopes characterized by different combination of two dynamic parameters, namely the internal areal heat capacity κ1 and the decrement factor f. An on-site monitoring campaign was extensively performed, during summer and winter seasons, on an unoccupied and windowless test room in Central Italy. Four internal linings were simultaneously tested on the south facing wall: plasterboard (as a baseline reference), two dry clay panels with different thickness and a combination of brick and an additional internal insulation layer. Over the year, the indoor microclimate was exposed to three different occupancy/solar gains profiles, identified with Test 1–3 and supplied to the room by three electric radiators. During Test 1 and Test 2 (summer and autumn, respectively), the results have shown the limits of the adoption of lightweight and hyper-insulated external walls with high internal areal heat capacity and very low decrement factor in the Mediterranean area. In fact, such typology exhibits the highest surface temperatures, with daily maximum around 28 °C and nocturnal minimum approximately 1.5 °C lower. Moreover, increasing the thermal resistance of a wall by adding an insulated lining partially inhibits the proper storage ability on the inner side, causing the release of more heat inside the test room. Conversely in winter (Test 3), such configuration was found to have a positive response in terms of stored heat quota, with respect to the released one. The solution that guaranteed the best thermal performance on annual basis under different indoor boundary cond